The 49-year-old star, who adopted Connor and Isabella with her ex-husband Tom Cruise, said she can totally relate to the film's plot, reported Entertainment Tonight.
"I can see now, for 'Lion,' that it was important to me because I'm a mother with adopted children," Kidman said.
The actress plays a mother in the film, who adopts her son from India after he is found on the streets of Kolkata.
"This movie is a love letter to my children. (My character) Sue is deeply maternal and full of unconditional love, which is beautiful.